The nature of dark matter has been debated for years. Now, some physicists believe a simple theory may explain it. They've suggested that most of the matter in the universe may be made out of particles that possess an unusual, doughnut-shaped electromagnetic field called an anapole, which means that dark matter would be endowed with a rare form of electromagnetism. This is a comparison of an anapole field with common electric and magnetic dipoles. The anapole field, top, is generated by a toroidal electrical current. As a result, the field is confined within the torus, instead of spreading out like the fields generated by conventional electric and magnetic dipoles. (Photo : Michael Smeltzer, Vanderbilt University)

The nature of dark matter has been debated for years. Now, some scientists believe they know how dark matter really acts. They've suggested that most of the matter in the universe may be made out of particles that possess an unusual, doughnut-shaped electromagnetic field called an anapole, which means that dark matter would be endowed with a rare form of electromagnetism.

In the past, several physicists have suggested that dark matter is made from Majorana fermion particles. Yet while this particle was predicted in the 1930s, it's stubbornly resisted detection. The new study also suggests that dark matter is made out of these particles, but this time the scientists may have some proof.

Fermions are particles like the electron and quark, which are the building blocks of matter. Since they were first suggested in 1928, physicists have been hunting for this elusive particle. So far, the prime candidate has been the neutrino, but scientists have been unable to determine the basic nature of this secretive particle.

This latest study, though, may have finally solved the mystery of dark matter and Fermions. The researchers performed calculations that actually demonstrated that these particles are uniquely suited to possess the doughnut-shaped anapole. This electromagnetic field gives them properties that differ from those of particles that possess the more common fields, such as those possessing two poles, and explains why they're so difficult to detect.

"Most models for dark matter assume that it interacts through exotic forces that we do not encounter in everyday life," said Rober Scherrer, one of the researchers, in a news release. "Anapole dark matter makes use of ordinary electromagnetism that you learned about in school--the same force that makes magnets stick to your refrigerator or makes a balloon rubbed on your hair stick to the ceiling."

Recently, though, researchers have discovered dark matter particles that don't carry electrical charges, but instead have electric or magnetic dipoles. The only issue is that even these more complicated models are ruled out for Majorana particles, which is why the scientists in this study took a closer look at dark matter with an anapole magnetic moment.

"Although Majorana fermions are electrically neutral, fundamental symmetries of nature forbid them from acquiring any electromagnetic properties except the anapole," said Chiu Man Ho, one of the researchers, in a news release.

Particles with an anapole must be moving before they interact; the faster they move, the stronger the interaction. That means that anapole particles would have been much more interactive during the early days of the universe, and would have become less interactive once the universe expanded and cooled. In fact, the anapole dark matters particles suggested by this study would annihilate in the early universe just like other dark matter particles. The leftovers from this process would form the dark matter that we see today.